In the technology information age today computers have been indispensable in people's life. Almost every line of business has to rely on computers to aid operation, either desktop computers or notebook computers. The application scope and use time are extensive. They could be used in any environments. However, in a low luminosity or dark environment, not sufficient light often causes inaccurate keystrokes and results in erroneous signal output. To solve such a problem many types of illuminated keyboards have been developed, such as U.S. Pat. Nos. 6,179,432, 6,199,996, 6,284,988, 6,322,229 and 6,554,442. They all disclose an illuminated keyboard which mainly has a lighting sheet held in the keyboard to illuminate keycaps to facilitate user operation of the keyboard in a light-deficient or dark environment.
However, the aforesaid techniques mostly have an elastic element and a moving mechanism interposed between the lighting element and keycaps. The keycaps, elastic element and moving mechanism are mostly made of light permeable material (some of the techniques have the keycaps made of an opaque material with the character portion on the keycaps made of the light permeable material). When the entire lighting sheet emits light the keyboard is evenly illuminated in a backlit manner. Such an illuminated keyboard generally is used in a light-deficient or dark environment, such as in an airplane, vehicle or the like. But with the entire keyboard emitting light evenly the total luminosity is too strong that could affect people nearby. Moreover, in the lower luminosity environment user's visual capability on the keyboard is lower naturally, with the entire keyboard luminous evenly user is difficult to differentiate the character notation of each keycap. Even through the characters and symbols are made of opaque material, or the keycap is made of impermeable material while the character notation made of permeable material, light emitting from the gaps between the adjacent keycaps still make the user hard to recognize the characters. For a user who does not well memorize location of the characters the situation is particularly serious, and he may thus input wrong instructions.